The main problem that I see with the Purge is that it doesn’t seem to have an internally consistent and coherent design. The way it is right now, it’s not really clear what its purpose is.
When it first got introduced, it was understood that it would provide some kind of tension or limiting force with regards to building on PVE servers. The idea was not to prevent people from building, but to introduce some kind of risk.
Then, at some point, they introduced Purge-only thralls. Suddenly, the Purge pivoted from a limiter to a risk-and-reward system.
Right now, it’s really weird. From what I’ve been able to see, the Purge meter seems to react a lot more to what you’ve been killing and the thralls you’ve been breaking on the wheel, than to what you’ve built. It’s also very hard to get it to trigger if you haven’t clanned up with at least one more player. So it definitely doesn’t seem to be meant as a limiter anymore.
Thing is, it doesn’t work as a challenge/reward system, either. The only reward you can get from the Purge is a Purge-only thrall, and you only get those from human purges. Now, human purges are difficulty 4. Official servers are set to difficulty 6. In theory, that means that you should have a chance of getting a Purge of any difficulty from 1-6, but in practice, it means vast regions of the map never get human Purges.
Even if we consider that to be a bug, and they fix it eventually, the way it “should” work according to Funcom is still flawed: setting the Purge difficulty to 6 means that the chance of getting the reward is lower. That might sound fine, but it isn’t, because this probability is a binary setting for the whole Purge: when you get Purged, you will either get a human Purge or you won’t; yes or no, on or off, that’s it.
On top of that all, there’s your original complaint that the Purge will spawn inside a base if the algorithm doesn’t “like” your base. And I use the word “like”, because I’ve had Purges spawn inside a base built on perfectly flat and accessible ground, with no disconnected bits or anything weird like that. For some reason, the algorithm couldn’t handle my base well and just shrugged and spawned enemies in my courtyard – fully paved, fully connected courtyard.
So what are we left with? Confusion. Take a few good but contradictory ideas, mash them together haphazardly, implement the resulting design poorly and you get the Purge as we have it.